Production of solid carbon dioxide



Nov. 12, 1935. ca. MAIURI PRODUCTION OF SOLID CARBON DIOXIDE Filed June20, 1935 2 Sheets-Sheet l I/VVf/VTOR GUIDO MEN/RI Nov. 12. 1935. e.MAIURI PRODUC'I'ION 0F SOLID CARBON DIOXIDE Filed June 20, 1935 2Sheets-Sheet 2 Patented Nov. .12, 1935 PATENT OFFICE PRODUCTION OF SOLIDCARBON DIOXIDE Guido Maiuri, Torino,

Italy, assis'nor to Maiuri Refrigeration Patents Limited, Aldwych,London, England Application June 20, 1933, Serial No. 676,623

InG

Claims.

This invention relates to the production of solid carbon dioxide orcarbon dioxide snow.

Carbon dioxide gas can be produced by various methods, amongst which isby the combustion of coke in an excess of air, the air being in excessto avoid the ultimate presence of carbon mon-' I oxide. The products ofsuch combustion consist of carbon dioxide and nitrogen, together with asmall quantity of oxygen due to the air being in excess. The carbondioxide is separated by being absorbed in a soda solution, from which itis driven off by heat.

To obtain solid carbon dioxide, usually gaseous carbon dioxide iscompressed in a multistage compressor and by the expansion of part ofthe compressed carbon dioxide, the remainder is eventual- 1y frozen intothe solid condition as carbon dioxide snow.

The object of the present invention is to enable solid carbon dioxide tobe produced from. carbon dioxide gas, of whatever origin, without theemployment of a multistage compressor, which is an expensive machine,and with a lesser expenditure of energy than with a multistagecompressor.

For the above purpose, according to the invention, in the production ofsolid carbon dioxide the latent heat of vaporization of the carbondioxide is removed from the carbon dioxide in an absorptionrefrigerating machine.

The use of an absorption refrigerating machinefor the above purpose hasadvantages over other types of refrigerating machines in respect of sizeand economy of working.

Preferably, the carbon dioxide is maintained above its triple pointpressure in the absorption refrigerating machine so that it passesthrough the liquid state before solidifying inside or outside themachine. This avoids the deposit of carbon dioxide snow within themachine and the accompanying troublesome removal of such snow. Thetriple point of carbon dioxide, (viz. the temperature and pressure atwhich it can co-exist in the gaseous, liquid and solid state inthermodynamic equilibrium) is -56.6 C. at 5.28 kilogrammes per squarecentimetre.

The carbon dioxide can be maintained above its triple point either inrespect of both pressure and temperature or in respect of pressure only.

For example, the carbon dioxide gas can be compressed in a single stagecompressor to 6 kilogrammes per square centimetre (6 atmospheres real;Britain June 30, 1932 atmospheric pressure, whereupon part thereofevaporates and expands, and the temperature decreases to 78.9 0., whichis the freezing point of carbon dioxide at atmospheric pressure. At thistemperature of 78.9 0., about 58% of the car: bon dioxide solidifies ascarbon dioxide snow, with a loss of 42% which has evaporated to theaseous state.

The carbon dioxide snow can, in the known manner, be consolidated intocarbon dioxide ice by mechanical pressure.

Alternatively, carbon dioxide gas compressed to 4 atmospheres absoluteiscooled in an absorption refrigerating machine to about C. At thispressure the carbon dioxide freezes into snow without passage throughthe .liquid state. On allowing the snow at 60 C. and 4 atmospheres topass to a region at atmospheric pressure, some evaporates and expandsand the resulting expansion reduces the temperature to -78.9 C. 20 andall but about 5% of the carbon dioxide re .mains as carbon dioxide snow.

In a further alternative, with a refrigerating machine giving atemperature of 60 0., carbon dioxide compressed to 6 atmospheres can becool- 25 ed to about 53" 0., the liquefaction point at 6 atmospheres,and passed in the gaseous state at said pressure into moulds, cooled bythe refrigerating machine at 60 C. In these cooled moulds the carbondioxide freezes into ice passing for 30 ashort time through the liquidstate and forming solid blocks of high density. Instead of compressingthe carbon dioxide gas in a mechanical compressor, it can be maintainedat the required pressure, for instance slightly 35 above the triplepoint pressure, by pressure generated in a boiler, as hereinafterdescribed.

Not only do the above methods of producing solid carbon dioxide avoidthe use of expensive compressors and the incidental large expenditure 40of mechanical energy, but also the heat required for operating theabsorption refrigerating machines and for driving the carbon dioxide gasout of the soda solution, can be obtained from the combustion of coke toproduce the carbon dioxide 45 gas. Likewise the heat can be used togenerate steam for a steam engine driving the single stage compressor.

It has been estimated that whereas by threestage compression it isnecessary in compressing 50 263 kilogrammes per hour of CO: gas toobtain 38% or kilogrammes of carbon dioxide snow to expend 40 H. P.,with the first method according to the invention 100 kilogrammes of snowper hour can be obtained by compressing kilol 95% of the gas treatedbeing converted into snow.

Expanded carbon 'dioxide gas at 478.9 C. is

obviously returned to the compressor, after having in the heatexchangerextracted heat from carbon dioxide gas @atB or 4 atmospheres, as thecase may be,'goi'ng to the evaporator of the refrigerating machine.

Plants for carrying out the invention are diagrammatically illustratedby way of example on the accompanying drawings, in which:--

Fig. 1 is a diagrammatic sectional elevation of a plant for makingcarbon dioxide snow with a one-stage compressor and an absorptionrefrigerating machine. i

Fig. 2 is a diagrammatic sectional elevation of a plant for makingcarbon dioxide ice with an absorption refrigerating machine and in whichboiler pressure is employed to maintain the carbon dioxide underpressure.

Referring to Fig. l, a is the furnace of a boiler b. The products of thecombustion of coke in the furnace a pass, by a pipe 0, into a scrubber(1, wherein the water and other condensible constituents of the productsof combustion are condensed, and the gases are freed from dust and othermechanical impurities. From the scrubber d the carbon dioxide andnitrogen constituents of the products of combustion unabsorbed by thewater in the scrubber, pass by a pipe c into an absorption column fwherein the carbon dioxide is absorbed by a descending shower of sodasolution. The nitrogen escapes through a chimney p p J The soda solutionwith the carbon dioxide dissolved therein flows down a pipe 9 through aheat exchanger g to a sprinkler g at the top of a heated chamber 9containing bames g.

The soda solution is drawn-off from. the bottom of the separatingchamber g through a pipe g by a pump 9, passing thereto through the heatexchanger 9. The pump g delivers the soda solution to a sprinkler I atthe top of the absorption column f.

The carbon dioxide is driven-oh from the soda solution by the heat inthe chamber g and, to gether with water vapour, passes by a pipe 11 to aheat exchanger h and thence by a pipe i to a water-cooled cooler i. Thewater condensed in the cooler 1 passes out by a water trap i".

From the cooler i the carbon dioxide passes through a pipe i to a singlestage compressor 1' wherein it is compressed to 6 atmospheres abso.--

lute.

The compressed carbon dioxide gas passes from the compressor 7' by apipe k: to a water-cooled cooler is, from which it passes by a pipe 1 toa heat exchanger}, through which expanded carbon dioxide gas alsopasses, as described later.

From the heat exchanger 1 the compressed carbon dioxide gas passes by apipe m into the refrigerating chamber m of an absorption refrigeratingmachine.

The refrigerating chamber 1 is indicated as jacketing the evaporatorcoil n of the refrigerat an oys nozzle p into a chamber 9, which is atatmos pheric pressure.

Being at atmospheric pressure, part of the escaping liquid carbondioxide evaporates and expands and produces the temperature of -78.9 C.5 whereby a portion of the carbon dioxide freezes as carbon dioxide snowin the chamber p. Snow is formed instead of ice as the freezingparticles of liquid are all separated by expanding gas.

The carbon dioxide snow can be mechanically w compacted into dense solidcarbon dioxide.

Theresidue, of the expanded very cold carbon dioxide gas passes from thechamber p by a pipe I? to the above mentioned heat exchanger Z, whereinit cools' thef compressed carbon dioxide 15 gas proceedingtotherefrigerating chamber m.

From the heat exchanger 2 the carbon dioxide gas passes by a pipe 7"back to the compressor i, therein to become again compressed togetherwith fresh carbon dioxide gas arriving by the 20 pip 1- i q is thegenerator of the absorption refrigerating machine, of which n is thealready mentioned evaporator, r is the condenser and s is the absorberof this absorption refrigerating machine.

The above-mentioned heat exchanger h is located in a portion of thegenerator q of the absorption refrigerating machine, wherein latent heatof condensation of the water vapour arriving by the pipe h is utilized.

The already mentioned boiler to which is heated by the furnacea whichgenerates the carbon dioxide gas, is utilized to produce steam at say 2kilogrammes per square centimetre, (2 atmospheres absolute). This steamis supplied by piping t to heating coils t located in the separator gand in the generator q of the absorption refrigerating machine.Condensed water from the coils it flows by piping u to a sump u, fromwhich it is raised up a pipe v by a pump 12, which delivers it by a pipe1: back to the boiler b.

Steam from the boiler b if produced in sufllcient quantity and at asufficient pressure can also be supplied to a steam engine for drivingthe compressor 7'. If in such case an excess of carbon dioxide isproduced in the furnace a, such excess will be rejected by the soda.solution in the column becoming saturated, and will escape by thechimney pipe 1.

The plant illustrated in Fig. 2, differs from that of Fig. 1, mainly inthat the pressure above the triple point of the carbon dioxide ismaintained by pressure generated in the boiler b, and that the carbondioxide is cooled to the liquid state and sets as ice in moulds in theabsorption reirigerating machine. Thus in the plant illustrated in Fig.2, the soda solution which has absorbed carbon dioxide in the absorptioncolumn I, is forced by a pump u through the heat exchanger o and througha pipe 22 to the boiler b, wherein the carbon dioxide is driven off fromthe soda solution and a pressure of 6 atmospheres absolute ismaintained. The soda solution returns from the boiler b along a pipe 10to the heat exchanger a, from which it is delivered back to thesprinkler I in the absorption column 1.

Carbon dioxide gas and steam at 6 atmospheres absolute pass by a pipe:1: to the heating coll t of the generator q of the absorptionrefrigerating machine. In the coil t almost all the steam is condensedand its latent heat utilized to heat the generator q. The water ofcondensation in the coil t flows into a collector u from which itpassesalong, a pipe z, having a regulating cock' 2, to the heat exchanger a,where it mixes with soda solution proceeding from the boiler b to thesprinkler 1 of the absorption column 1'.

The carbon dioxide gas at 8 atmospheres and accompanied by the residueof the steam, passes frozen out of the carbon dioxide gas. The precoolerb may be duplicated, one being used to freeze-out the moisture whilstthe frozen-out moisture in the other is thawing and being drained-ed, Ig

The carbon dioxide gas atfi atmospheres absolute passes from thepre-cooler 5 into a portion 5 of the refrigerator wherein it is cooledto about 53 C., whichis the liquefaction point of carbon dioxide at 6atmospheres absolute. The so-cooled carbon dioxide-is admitted by cocks7 into a series 01 ranges of moulds 8. These moulds 8 are cooled, by anevaporator chamber Q of the absorption refrigerating machine, to 60 C.or to a lower temperature.

The carbon dioxide still at the pressure of 6 atmospheres absolute,which is above the triple point,becornes solidified in the moulds 8,passing momentarily through the liquid state, whereby the Ireezing inthe moulds occurs in stratified dense solid blocks.

As and when each mould 8 is estimated to be filled with a solid blockof- Irozen carbon diox ide, the respective cock I is closed, and thepressure in the mould is allowed to diminish to 1 atmosphere absolute.About 5% of the carbon dioxide thereupon evaporates and reduces thetemperature the remainder to the freezing point of carbon dioxide atatmospheric pressure,

viz. 78.9 C.

'The blocks of solid carbon dioxide or dry ice are extracted from themoulds and stored or delivered for sale.

Water is supplied to the various water-cooled portions of the plants andto the scrubber d of each plant by pipes I0.

I claim: 1. A method of producing a dense block of solid carbon dioxide,consisting in absorbing carbondioxide in an absorption medium, drivingof! by heat said carbon dioxide and vaporized absorption medium fromsaid absorption medium, utilizing the sensible heat oi said driven-oficarbon dioxide and the sensible and latent heat of said vaporizedabsorption medium as the prime mover oi a refrigerating system,compressing said driven-oi! carbon dioxide to slightly above its triplepoint pressure, and cooling said com- 10 pressed carbon dioxide by saidrefrigerating systern to a solidifying temperature.

2. A method of producing a dense block oi solid carbon dioxide,consisting .in absorbing carbon dioxide in an absorption medium, driving16 oil by heat said carbon dioxide at slightly above its triple pointpressure and vaporized absorption medium from said absorption medium,uti= lizing the sensible heat or said driven-on carbon dioxide and thesenslble and latent heat of said 20 vaporized absorption medium as theprime mover of a refrigerating system, and cooling said compressedcarbon dioxide by said refrigerating system to a solidifyingtemperature.

3. A method of producing solid carbon dioxide, consisting in absorbingcarbon dioxide in an absorption. medium, driving off by heat said carbondioxide and vaporized absorption medium from said absorption medium,utilizing the sensible heat 01 said driven-off carbon dioxide and thesensible and latent heat of saidvaporized absorption medium as the'primemover of a reirigerating system, compressing said carbon dioxide toslightly above its triple point pressure, cooling said compressed carbondioxide by said reirigerating system to a liquei'ying temperature, andexposing said so-liquefied carbon dioxide to a lower pressure.

i. A method of producing a dense block oi carbon dioxide ice in a mould,consisting in maintaining carbon dioxide gas at slightly above itstriple point pressure in said mould, and cooling said carbon dioxide insaid mould to a solidifying temperature.

5. A method of producing a dense block of carbon dioxide ice in a mould,consisting in compressing carbon dioxide .gas to slightly above 'itstriple point pressure, continuously admitting said carbon dioxide gas atsaid pressure into said mould, and cooling said carbon dioxide in 59said mould to a solidiiying temperat

